1. Field of the Invention
The invention is related to electric storage batteries, and, in particular, to efficient methods for charging such batteries.
2. Description of the Related Art
The starter batteries in motor vehicles, generally lead acid batteries, are charged by the alternator, acting as a generator, whose voltage is limited by a controller to a preset maximum. The purpose of the controller is to limit the charging voltage applied to the vehicle battery, where possible, to a value below the voltage at commencement of gassing (gassing voltage), so that the battery electrolyte decomposition which starts when the gassing voltage is exceeded, and consequent loss of water and corrosion by deleterious overcharging, are avoided. Maintenance-free operation of vehicle batteries requires the electrical energy in the process of charging to be supplied at a voltage which if possible is below the gassing voltage. In any case, however, recharging of the battery should be achieved as quickly as possible.
Usually the controller is set so as always to limit the charging voltage to a fixed maximum value. Since, however, the gassing voltage of the lead acid battery normally designated as the starter battery depends on the temperature, and the temperature of the battery can fluctuate within wide limits, depending on the season and the operational state of the vehicle, a fixed preset charging voltage maximum does not guarantee recharging in the shortest possible time without gassing under all temperature conditions. To compensate for temperature effects, temperature-dependent electronic circuits have previously been incorporated into the charging circuit between the battery and the alternator.
Such an arrangement is described, for example, in German Patent DE-C-2056045. However, these customary control methods are unsuitable for ensuring the highest possible charge state of the storage battery at all times. Consequently, a great variety of devices for monitoring the charge state of a starter battery had previously been proposed; for example, German Patent DE-C-3330953 describes a device which involves drawing up the current balance in the overall system and thus allowing the exact charge state of the storage cell to be controlled. This known device is complicated, however, and has therefore hitherto been virtually ignored in conventional motor vehicles.